Method of and means for felting with variable suction



Nov. 17, 1959 J. R. ROBERTS METHOD OF AND MEANS FOR FELTING WITHVARIABLE SUCTION Filed Jan. :50. 1953 2 Sheets-Sheet 1 7/ I lm/HES/STANCES "50C 7'/0/V BOX P/IES SURE 25 30 kssq F7551? SUSPENS/O/V 6A5PRESSURE I. LJ

fiarney Nov. 17, 1959 .1. R. RQEERTS 2,912,723

METHOD OF AND MEANS FOR FELTING WITH VARIABLE SUCTION Filed Jan. 50.1953 2 Sheets-Sheet 2 a7 a6 65 a4 a9 a2 19/ oo o c o oo 0 80-0000 0 a Oo o o o 000 00 o 6 0e j 0000 ooaooooo an ace 0 o- 000 0000 o 0 To:00000000 to? one a o 0000 00 o 0 O H c Jamesfijioerls O00 o [for UnitedStates Patent AND MEANS FOR FELTING WITH VARIABLE SUCTION James R.Roberts, Longview, haeuser Timber Company, tion of -Washington METHOD onWash., assignor to Weyer- Tacoma, Wash., a corpora- The presentinvention relates generally to felting fibers from gaseous suspensiononto a continuously moving filtering conveyer passing through adeposition area. In particular it relates to such felting bydilferential air pressure on the two sides of the conveyer, for examplesubatmospheric pressure on one side and atmospheric or superatmosphericpressure on the other.

Fibers have long been felted from air suspension on plane stretches ofendless screen conveyers and on rotating cylindrical screens orcondensers at relatively stationary deposition areas having anappreciable dimension along the direction of the moving filter. At oneboundary of this area the felt is initially begun on the bare filter,and at the opposite boundary the felt receives its last depositedmaterial, the vehicular air passing through a changing thickness of thefunctioning filter consisting conventionally of the screen and thevarying felt as it isformed. As a consequence the formation varies from'face to face as a result of growing resistance in the filter from theinitial zone to the end zone of formation, assuming of coursesubstantially constant pressure conditions on each side of thefunctioning filter. This is illustrated by an open suction boxunderlying a moving screen and by'a suspension of fibers at atmosphericpressure exposed to the screen over the suction box. In thisillustration the differential pressure through the filter is uniform,but the resistance to air passage varies progressively according to thethickness of the felt locally. This results in a greater volume of air,and hence heavier deposition and closer formation, at the local regionsof lower resistance. The present invention aims to overcome variationsin felt formation due to the variance in deposition resulting fromchanging resistance in the felt.

' It is a particular object locally to vary at least one of the terminalpressures at the faces of the functioning filter to maintain oversubstantially all of the deposition area a constant rate of deposition,so that all of the deposition takes place under the same conditions withresulting uniformity of formation from face to face.

It is another object of the invention to vary or control mat formationby locally controlling the various differential pressures to securevarious desired formations within the initially deposited felt.

Various other and ancillary objects and advantages of the invention willbecome apparent from the following description and explanation of theinvention as it may bepracticed with numerous variations.

In the accompanying drawings:

Fig. 1 is a diagrammatic electrical analog of illustrative feltingconditions to facilitate explanation and understanding of the invention.

Fig. 2 is a diagrammatic illustration of a simple felting process bywhich fibers in suspension at atmospheric pressure settle toward amoving screen in a deposition area over a suction box under thescreen,with intervening added resistances.

Fig. 3 is a detailed fragmentary 1 view in vertical cross section toillustrate variable perforations in cover plates to provide the variableresistances.

Fig. 4 is a view of another form of felter in which fibers are dispersedfrom superatmospheric pressure as a depositing column over a movingscreen under which there is a suction box encompassing the depositionarea, said suction box being provided with variable cover resistances.

Fig. 5 is a view showing more generally the character of the felter ofFig. 4.

Fig. 6 is a fragmentary plan view showing one type of resistance coverplates over the suction box of Fig. 4.

In the manufacture of pressed fiber products by compression of air-laidmats in accordance with the abovementioned conventional prior artmethods, variations in the initial mat formation from face to face ofthe mat are produced which are reflected in different properties atdifferent levels within the compressed product. Especially the facelayers of such compressed product may exhibit greatly divergentproperties, whereas it is frequently desirable that such pressedproducts be free from two-sidedness. The present invention is thereforevery useful in forming uniform air-laid fiber mats which are latersubjected to consolidation, usually in the presence of a binder whichpermanently integrates the fibers, as for example, into hot-pressedsynthetic fiber board exceeding natural wood in density and consistingprimarily of felted fibers bonded with thermosetting resin. However, theinvention is not at all limited to such field and has application inmany fields, such as the manufacture of cotton batting, fiber insulationand packing, insulation board, filtering cloths and papers, air filters,oil filters and the like.

The flow of vehicular air to deposit fibers is caused primarily by theair pressure gradient across the felting system. Hence, varying one orboth of the terminal pressures is an effective control of rate of flow,for any fixed resistance. Since the conventional practices employ tworegions of fixed terminal pressures at the deposition area, and becausethe growing mat adds resistance to air flow, the practical control is tocontrol resistance. This is readily done by combining filteringresistance with added resistance.

To explain this practical control, reference is made to an electricalanalog in Fig. 1. Numeral 10 is a battery having voltage E. This iscomparable to the differential air pressure. in felting. A closedcircuit 11 to the battery carries current I, predetermined by thecircuit resistance R. Resistance R consists of parallel lines 12 to 17of resistances, six lines being chosen to illustrate a greater, numberand even an infinite number, each to be compared later with lines orlocal regions of the filter of this invention. Each resistance linecontains three different resistances in series, designated a, b and c.All the b-resistances are equal. The amount of current i flowing in eachresistance line is predetermined by the resistance a+b+c in its line.

The resistances a correspond to the growing resistance of a mat assumingthat it begins on a screen at line 12 and is finished at line 17. Theresistances b are the constant resistance imposed by the screen. Theresistances c are such in each line that a+b+c= constant k, wherebycurrent i is the same in each line.

'Transposing this analog to a conventional felting on a screen over asuction box from constant terminal pres sures, it is apparent that equalrates of deposition over every local region of the deposition area maybe achieved by selection of resistances c for equalizing the totalresistances locally.

In a continuous felting of a mat on a moving conveyor, every localregion of the deposition area corresponds to an exact lengthwisecontinuous region in the felt in fixed position between the mat faces.By control of the rate of flow at any local area a select portion of themat may be controlled as to its formation. Of course, the effect of suchcontrol in one area on the superlying portion of the mat must beconsidered and may call for a series of changes or controls.

The invention, therefore, may be used for a great variety of purposes.For example, and preferably, it may be used to form a mat by a constantrate of deposition of the same fibers throughout all the deposition.Thus, the two face layers and all the inner regions have the sameformation. It may be used with disregard of the inner regions, andmerely to provide the two face layers with the same formation.

If desired variations along lines crosswise of the moving conveyer maybe made, so that, for example, there may be a change in formation fromone edge of the formed web to the other.

Because of the possibly complicated effect of a change in one localregion upon those ensuing regions which deposit over it, the desiredresults are best achieved by cut-and-try methods. Where the control iseffected by selected added resistance, the cut-andtry method of choosingthe resistance is simple and effective, and in practice may call simplyfor variously perforated plates under the screen However, it is a meansto the broader objective of controlling locally the differentialpressure which is effective across the functioning filter, whichpressure is the active control over the rate of flow of air, and hencethe rate of deposition.

Returning to the electrical analog for an equal overall rate ofdeposition, it is seen that at the region (line 12) of initialdeposition of the fibers on the base screen, the resistance a12 is zero,and the resistance -12 must at least equal the resistance 41-17 of thefinally formed mat at line 17. Where there is a resistance 0 at the lastline of deposition (electrical line 17) the resistance cl2 must besubstantially equal to mat-resistance a17 plus added resistance 0-17.

Fig. 2 shows a large gravity deposition chamber into which fibers areintroduced for gravity fall through air at atmospheric pressure. It hasa chamber 20 open to atmospheric pressure with front wall 21, rear Wall22 and side walls 23. The chamber is positioned over the upper stretchof an endless wire screen 25 passing over rollers, such as end roll 26,on which screen the felt F is to be formed. High in the chamber there isa horizontal sifting rack or screen 28 suitably open, so that in rapidhorizontal reciprocation it sifts fibers 29 from its loose load 30. Aneccentric drive 31 is connected by rods 32 to the rack 28 to provide thesifting reciprocation. Arrows 33 variously dispersed above the rack 18illustrate suitable means (not shown) to maintain an equalized supply offiber for load 31) on the rack.

Below the chamber 20 and encompassing a deposition area which is thebottom of said chamber 20, is a suction box 34 connected by conduit 35to a suction device such as the intake of a blower 36 operated tomaintain a substantially constant subatmospheric pressure in the suctionbox 34.

The top of the suction box adjacent the screen 25 is provided with acover. As shown, the cover consists of numerous individual plates 37easily removable and interchangeable. These plates 37 are strips runningcrosswise of the moving conveyor. The plates 37 are so mounted that theyprovide a plane or platform support for the screen 25 and they may bevariously pervious, or in some cases impervious, to the passage of airinto suction box 34. The felt F as it is being formed as shown withinthe deposition area has an inclined plane as its forming top, resultingfrom a uniform accumulation of fibers as the screen advances at a fixedrate through a uniform shower of fibers 29. For convenience the coverplate 37 at the beginning edge of the felt is designated 37 and that atthe finishing edge of the felt is designated 37.

The plate 37 is but slightly perforated to provide resistance to airflow, the resistance being uniform crosswise of the conveyer. There arealso perforations in plate 37*, which is more open than plate 37 tooffer less resistance to air flow. During felt formation as illustrated,the total resistance at every given area is the same and consists of theresistance of the cover plate at that area, the resistance of the screen25 and the resistance of the formed felt over the area. The plates 37between the terminal plates 37 and 37 are therefore open or perforatedand the resistance is properly graduated downwardly from plate 37 toplate 37', so that the growing top 38 of the felt is an inclined plane.

Fig. 3 is merely exemplary of graduated resistance, without signifyingthat the illustrated proportions are exact for the incline planedescribed. The plates 37 are shown as together providing a platform forscreen 25'. T be open space in the mesh on the underside of screen 25 issufficient to distribute the suction generally about each opening. Thisdistribution and the general advance of the screen minimize the effectof distance between perforations.

By reason of the rack 28 being so constructed and operated as to supplya substantially uniform concentration of falling fibers over the areaand by reason of the added resistances at the suction box, the formationof the felt is the same from beginning to end and. hence from face toface, because the fibers deposit on all areas with the same rates, withthe same randomness of orientation and with the same impact.

The invention is likewise applicable to felting operations in which thegas in which the fibers are suspended is at superatmospheric pressure oris variable over the deposition area from atmospheric pressure tosuperatmosphen'c pressure. Such an apparatus is illustrated in Figs. 4and 5. The numeral 40 designates a semi-cylindrical dispersing head atthe bottom end of a vertical column comprising a box-like section 41just above the head 40-, and an upwardly tapering extension 42functioning. as an expansion conduit or chamber. The top of the chamber42 is connected to a conduit elbow 4-3 which leads downwardly at anincline by way ofa straight and long conduit 44 to the discharge side ofa blower 45. The intake side of the blower 45 is designated 46 and drawsair from. the atmosphere at a hopper-like opening 47. Into. theopening47 a supply of fiber 48 is fed at a constant rate by means not shown.

In the dispersing head 40 there is a coaxial rotary agi-' tatordesignated 50 operating at high. speed to maintaina supply of fibers inthe headwell. dispersed and. in agita-- tion. A squirrel-cage type ofrotor is suitable with its bars 51 provided with brist1es52, to sweepfibers through openings in. the head 40. The. lower arcuate= portion 55of the head 40 is perforated, for example over. an. arc of about with.fiber-dispersing. holes 56. arranged, uni.- formly lengthwise alonggeometrical elements. of the cylindrical head, but. not necessarilyuniformly in. adjacent. elements. In operation the fibers in. the head40 are at superatmospheric. pressure. and by means. of the rotor 50 theyare evenly dispersed and discharged along. said elements and through theperforations 56, forming a column of fiber suspension moving. downwardlytoward a suitable filtering conveyer to form a felt. thereon.

A moving endless wire screen. has its upper stretch. 6ft move under saidhead 40 from/ end roll 61. Beneath the upper stretch 60 of the screen.there is a suction. box. 63 connected by conduit 64 to the suctionsideof a blower 65 discharging against atmospheric pressure. The suc-- tionbox 63 is preferably made to encompass.- an area. somewhat greater than.the projected area of. the head 40 on the screenv which makes. possible;the planned. varia' tions in product properties because of. the variablecontrols. The top of the suction box is provided with resistance plates67 in the general manner previously described with referencetot Figs. 2and3.

. rying gaseous vehicle.

There may. be provided a vertical baffle 68 extending downwardly betweenside walls 69 from the semi-cylindrical head 40 substantially to thewire screen 60 in order to define a clear-cut boundary line for thebeginning of felt formation. In furtherance of this objective, the coverplates or plate 67 over that portion of the suction box to the rear ofthe baffle 68 may be impervious to render suction non-effective. Thiscover portion 67 may be perforated to a minor degree if it is desired tocatch by suction such fibers as may bleed out of space 70 between thebottom edge of the baffle 68 and the screen 60. The plates 67 in thedirection of felt formation are variously perforated in accordance withthe kind of formation desired. Whereas Fig. 2 illustrates formation ofthe felt by uniform deposition over the whole area, the plates of Fig. 4for the purpose of illustrating a modification, are so perforated thatdifferent rates of deposition, and hence different types of formation,may be effected. The forming face of the felt is illustrated by acontour line having end portion 72, a middle portion 73 and finalportion 74. The cover plates 67 on the suction box are, therefore,perforated to control the rates of depositions differently in thesethree zones. If desired, the lines 72 and 74 may represent the sameconditions so that the facial formations of the resulting felt 76 arethe same, and the central portion of the felt, corresponding to formingline 73, may be different in character, as the result of a greater rateof deposition indicated by the greater slope of line 73.

Fig. 6 is a plan view of a suction box cover to exemplify the range ofpossibilities. The dotted line 80 indicates the direction of feltformation over the cover comprising crosswise perforated plates 81through 87.

On each side of line 80 the resistance decreases in the direction offelt formation. Not only the spacing, but the size of the holes varies.With respect to the conditions described for Fig. 2, the length of eachplate is uniformly perforated. However, this need not be so in allcases. The plates 81-87 are each of different resistance values on thetwo sides of line 80, thus to form a felt having two different butintegrated felts.

From the foregoing it will be understood that the invention providesspecial controlling means for use in felting fibers on a continuouslymoving filter from a car- Not only may the said means be formed toproduce felts which have uniform formation from face to face, but it maybe used to create a variety of special felts, all as contemplated by theinvention as expressed in the appended claims.

I claim:

1. The method of felting which comprises contlnuously and relativelymoving a filtering conveyer through a relatively fixed deposition area,continuously maintaining in said area on one side of said conveyer agaseous suspension of feltable fibers at a substantially constant gaspressure, maintaining directly at the other side of said conveyer insaid area locally different and lower gas pressures, whereby thedifferential pressures over said area result in depositing a growingfelted mat on said conveyer in said area, and fixing the said localpressures for uniformity along lines crosswise of the conveyer inaccordance with the speed of the conveyer and growth of the mat tomaintain between the faces of the mat predetermined local differentialpressures, whereby to control the deposition locally in said area andthereby control the structure of the deposited mat.

2. The method of felting which comprises continuously and relativelymoving a filtering conveyer through'a relatively fixed deposition area,continuously maintaining in said area on one side of said conveyer agaseous suspension of feltable fibers at a substantially constant gaspressure, maintaining directly at the other side of said conveyer insaid area locally different and lower gas pressures, whereby thedifferential pressures over said area result in depositing a'growiugfelted mat on said conveyer in said area, and fixing the'said localpressuresfor uniformity along lines crosswise of the conveyer and fordifferences lengthwise of the conveyer in accordance with the speed ofthe conveyer and growth of the mat to maintain between the faces of themat predetermined local differential pressures along said lines, wherebyto control and to render uniform the deposition along each of said linesand thereby to vary and control the structure of the deposited mat fromface to face.

3. The method of felting which comprises continuously and relativelymoving a filtering conveyer through arelatively fixed deposition area,continuously maintaining in said area on one side of said conveyer agaseous suspension of feltable fibers at a substantially constant gaspressure, maintaining directly at the other side of said conveyer insaid area locally different and lower gas pressures, whereby thedifferential pressures over said area result in depositing a growingfelted maton said conveyer in said area, and fixing the said localpressures for uniformity along lines crosswise of the conveyer and forgraded differences lengthwise of the conveyer in accordance with thespeed of the conveyer and growth of the mat to maintain between thefaces of the mat predetermined local differential pressures, whereby tocontrol and to render uniform the deposition along each of said linesand to vary progressively and to control the structure of the depositedmat from face to face.

4. The method of felting which comprises continuously and relativelymoving a filtering conveyer through a relatively fixed deposition area,continuously maintaining in said area on one side of said conveyeragaseoussuspension of feltable fibers at a substantially constant gaspressure, maintaining directly at the other side of said conveyer insaid area locally different and lower gas pressures, whereby thedifferential pressures over said area results in depositing a growingfelted mat on saidconveyer in said area, and fixing the said localpressures for uniformity along lines crosswise of the conveyer and fordifference in the end zones of the length of said area along theconveyer in accordance with the speed of the conveyer and growth of themat to maintain between the faces of the mat predetermined localdifferential pressures, whereby to control and to render uniform thedeposition along each of said lines and thereby to vary the depositionand to control the structure of the facewise layers of the depositedmat.

5. The method of felting which comprises continuously and relativelymoving a filtering conveyer through a relatively fixed deposition area,continuously maintaining in said area on one side of said conveyer agaseous suspension of feltable fibers at a substantially constant gaspressure, maintaining directly at the other side of said conveyer insaid area locally different and lower gas pressures, whereby thedifferential pressures over said area result in depositing a growingfelted mat on said conveyer in said area, and fixing the said localpressures in accordance with the speed of the conveyer and growth of themat to maintain equally over said area a substantially uniform rate ofdeposition.

6. The method of felting which comprises continuously and relativelymoving a filtering conveyer through a relatively fixed deposition area,continuously maintaining locally in said area on one side of saidconveyer gaseous suspensions of feltable fibers each at substantiallyconstant conditions of fiber character, fiber concentration and gaspressure, maintaining directly at the other side of said conveyer insaid area locally different and lower gas pressures, whereby thedifferential pressures over said .area result in depositing a growingfelted mat on said conveyer in said area, and fixing the said lowerlocal pressures in accordance with the speed of the conveyer and growthof the mat to maintain locally over said area substantially the samerate of deposition.

7. The method of felting which comprises continuously and relativelymoving a filtering conveyer through a relatively-fixed deposition area,continuously maintaining lo cally inv said. area on one side of saidconveyer gaseous suspensions of feltable fibers each at substantiallyconstant conditions of fiber character, fiber concentration and gaspressure, maintaining directly at the other side of said conveyer insaid area locally different and lower gas pressures, whereby thedifferential pressures over said area result in. depositing a growingfelted mat on said conveyor in said area, and relatively fixing thecooperating local pressures on said two sides of the conveyer inaccordance with the speed of the conveyer and growth of the mat tomaintain locally over said area substantially the same rate ofdeposition;

8. The method of felting which comprises continuously and relativelymoving a filtering conveyer through a relatively fixed deposition area,continuously maintaining locally in said area on one side of saidconveyer and along lines crosswise of the conveyer gaseous suspensionsof feltable fibers each at substantially constant conditions of fibercharacter, fiber concentration and gas pressure, maintaining directly atthe other side of said conveyer in said area locally different and lowergas pressures uniformly crosswise of the conveyer, whereby thedifferential pressures over said area result in depositing a growingfelted mat on said conveyer in said area, and fixing the said. locallower pressures in accordance with the speed of the conveyer and growthof the mat to maintain along each line crosswise of the conveyersubstantially the same rate of deposition.

9. Themethod of felting which comprises continuously and relativelymoving a filtering conveyer through a relatively fixed deposition area,continuously maintaining locally inv said area on one side of saidconveyer and along lines crosswise of the conveyer gaseous suspensionsof feltable fibers each at substantially constant conditions of fibercharacter, fiber concentration and gas pressure, maintaining directly atthe other side of said conveyer in said area locally different and lowergas pressures, whereby the differential pressures over said area resultin depositing a growing felted mat on said conveyer in said area, andfixing the said local lower pressures in accordance with the speed ofthe conveyer and growth of the mat to maintain locally over said areasubstantially the same rate of deposition.

10. The method of felting which comprises continuously and relativelymoving a filtering conveyer through a relatively fixed deposition zone,continuously maintaining in said zone over one side of said conveyergaseous streams of suspended fiber to be deposited thereon, the two endregions of said zone extending crosswise of the conveyer and boundingsaid zone lengthwise of the conveyer having fiber suspensions each atsubstantially constant conditions of fiber character, fiberconcentration and gas pressure, maintaining directly at the other sideof said conveyer opposite said zone locally different and lower gaspressures, whereby the differential pressures within the area defined bysaid zone result in depositing a growing felted mat on said conveyer insaid zone, and fixing the said local lower pressures below said twosuspensions at said end regions in accordance with the speed of theconveyer and growth of the mat to maintain the same rate of depositionof the first and last deposited portions of the mat.

l]. The method of felting which comprises continuously and relativelymoving a filtering conveyer through a relatively fixed deposition area,continuously maintaining in said area on one side of said conveyer agaseous suspension of feltable fibers at a substantially constant gaspressure, maintaining on the other side of said conveyer in said area asubstantially constant and lower gas pressure, whereby the differentialpressure over said area results in depositing a growing felted mat onsaid conveyer in said area, and imposing resistances to air flow atlocal regions between said conveyer and said lower pressure region, thevalue of said resistances. being predetermined in accordance with thespeed of the conveyer and growth of the mat to maintain equally oversaid area. asubstantially uniform rate of deposition.

12. The method of felting which comprises continuously and relativelymoving a filtering conveyer through a relatively fixed deposition area,continuously maintaining in said area on one side of said conveyor agaseous suspension of feltable fibers at a substantially constant gaspressure, maintaining on the other side of said conveyer in said area asubstantially constant and lower gas pressure, whereby the differentialpressure over said area results in depositing a growing felted mat onsaid conveyer in said area, and imposing resistances to air flow atlocal regions along lines crosswise of the conveyer between saidconveyer and said lower pressure region, the value of said resistancesbeing predetermined in accordance with the speed of the conveyer andgrowth of the mat to maintain along said lines a substantially uniformrate of deposition.

13. The method of felting which comprises continuously and relativelymoving a filtering conveyer throughv a relatively fixed deposition area,continuously maintaining said area on one side of said conveyer agaseous suspension of feltable fibers at a substantially constant gaspressure, maintaining on the other side of said conveyer in said area asubstantially constant and lower gas pressure, whereby the differentialpressure over said area results in depositing a growing felted mat onsaid conveyer in said area, and imposing resistance to air flow at localregions between said conveyer and said lower pressure region includingthe conveyer-end-regions of said area, thevalue of the resistances atsaid end-regions being predetermined in accordance with the speed of theconveyer and growth of the mat to maintain in said end-regionssubstantially the same rate of deposition, whereby to render uniform thefirst and last deposited layers.

14. The method of felting which comprises continuously and relativelymoving a filtering conveyer through a relatively fixed deposition area,continuously maintaining in said area on one side of said conveyer agaseous suspension of feltable fibers at a Substantially constant gaspressure on each local region over said deposition area, maintaining onthe other side of said conveyer in said area a substantially constantand lower gas pressure, whereby the differential pressure over saiddeposition area results in depositing a growing felted mat on saidconveyer in said area, and imposing selected resistance to air flow atlocal regions between said conveyer and said lower pressure regionwhereby to control the rate of fiow of air at each local region of thedeposition area by the sum of the resistance of the growing mat at saidlocal region, the resistance of the conveyer and the imposed selectedresistance.

l5. Felting apparatus comprising in combination a movable filteringconveyer on which continuously to form an air-laid felt by differentialair pressure therethrough, means providing a continuous supply offeltable fibers in air suspension exposed to said conveyer at uniformconditions of concentration and air pressure at all local regions ofsaid supply over a deposition area on said conveyer, a suction box belowsaid conveyer encompassing said deposition area and positioned to drawair through said conveyer from said fiber suspension, means to maintaina substantially constant subatmosphere pressure in said suction box, andair-passing cover means between said suction box and said conveyer, saidcover means having a locally predetermined resistance to air flow, eachsaid local resistance being uniform across the direction of motion ofthe conveyer, and the local resistances varying in said direction,whereby at each local area the total resistance between the terminalpressures consists of the resistance in said cover means, in saidconveyer, and in the growing felt being formed thereon.

16. Felting apparatus comprising in combination a movable filteringconveyer on which continuously to form an air-laid felt by difierentialair pressure therethrough, means providing a continuous supply offeltable fibers in air suspension exposed to said conveyer at uniformconditions of concentration and air pressure at all local regions ofsaid supply over a deposition area on said conveyer, a suction box belowsaid conveyer encompassing said deposition area and positioned to drawair through said conveyer from said fiber suspension, means to maintaina substantially constant subatmospheric pressure in said suction box,and removable cover plates for said box interposed between the area ofsuction and said conveyer, said plates being perforated variously toprovide various reistances locally to air flow between the terminalpressures, whereby to control locally the 110w of air and fiber informing felt on said screen.

17. Apparatus for felting comprising a continuously movable filteringconveyer on which to form a fiber felt by filtration from a gaseoussuspension of fibers, means providing substantially constant butdifferent terminal gas pressures on both sides of said conveyer at adeposition area of said conveyer whereby the difierential pressurecauses flow of gas through said conveyer, means to maintain in thegaseous region at the higher pressure a substantially constant supply offibers in suspension at each local region, whereby the said flow of aircauses continuous deposition of fibers on said conveyer as the con veyermoves continuously, and air-passing means providing locally in saiddeposition area between said conveyer and said lower pressure gaseousregion predetermined resistance to air flow between said terminalpressures, each said local resistance being uniform across the direc- 107 tion of motion of the conveyer, and the local resistances varying insaid direction, whereby said local resistances may be selected andpredetermined in relation to the resistance offered "by the growingfelt.

18. Apparatus comprising means forming a continuously movable filteringconveyer on which to form a fiber felt from a gaseous suspension offiber moving toward a deposition zone at a first face of the conveyer, asuction box opening toward the second face of said, conveyer anddefining said deposition zone, means to create and continuously maintaina fixed pressure in said box, means continuously to provide a gaseoussuspension of fiber at a pressure above that in said box, saidsuspension being exposed to said first face for deposition of fibersthereon, and fixed means between said suction box and said second facefor the passage of air from said suspension into said box, said fixedmeans offering resistance to the flow of air therethrough, saidresistance varying locally in the direction of movement of the conveyerand being constant along lines crosswise of said direction.

References Cited in the file of this patent UNITED STATES PATENTS

